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Timer2 calculations

 
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MCUprogrammer



Joined: 08 Sep 2020
Posts: 92

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Timer2 calculations
PostPosted: Mon Mar 07, 2022 11:53 pm     Reply with quote

hello
PIC18F67J60 25MHZ

Timer Period = (1/((Fosc / 4) / T divisor) ) * (PR2 + 1)
I wrote the formula used to calculate the timer period. Well, I want the timer period value to be 10ms. Now, since the period value is certain, what kind of formula should I create? Can you talk about it?
So how do you decide to create the T divisor and PR2 values?
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MCUprogrammer
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temtronic



Joined: 01 Jul 2010
Posts: 8528
Location: Greensville,Ontario

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PostPosted: Tue Mar 08, 2022 6:19 am     Reply with quote

well, you could 'cheat'....
https://www.mikroe.com/timer-calculator
I've used it on and off for years..
with pres=1:16, psts=1:16, PR2=244 it computes to 9.9968ms

2.5 decades ago I wrote a QuickBasic4.5 program to 'do the math', I'd have to find my good old Win98SE machine to see just how I did it though...

Jay
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Tue Mar 08, 2022 11:44 am     Reply with quote

On divisor, remember PR2+1 maxes at 256.
So ((Fosc/4)/256)/F, gives you the value that divisor must be bigger than:

So for 100Hz (10msec):

((25MHz/4)/256)/100) =244

So (given the available divisors), 256 must be used.

Then with this, you get ((25MHz/4)/256)/100 gives PR2+1=244.
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